Fluid control devices related to the present invention are generally used in hydraulic control systems. A basic hydraulic control system includes a hydraulic cylinder for receiving hydraulic fluid and a piston that is moveably mounted inside the cylinder. Flow of hydraulic fluid into and out of the cylinder alters the pressure in the cylinder and thereby controls movement of the piston relative to the cylinder. Movement of the piston is typically used to control movement of a mechanical device, for example, a blade on a motor grader. Flow of hydraulic fluid out of the cylinder is generally accomplished by using a check valve. In addition, generally a pilot pressure operated relief valve is also connected to the cylinder to provide induced high pressure relief.
One problem associated with hydraulic cylinders is cylinder drift. Cylinder drift occurs when fluid leaks from the pressurized hydraulic cylinder. Cylinder drift tends to occur when the check valve is mounted near the main hydraulic valve to the cylinder.
One solution to minimizing cylinder drift has been to mount the check valve directly to the hydraulic cylinder. A cylinder mounted check valve acts as a lock to minimize fluid leakage and as a result it minimizes cylinder drift. One difficulty with the current cylinder mounted check valves is that they require routing of hydraulic pilot pressure control lines from the main valve to the cylinder mounted check valve. This routing of hydraulic pilot pressure control lines can make assembly difficult. In addition, there is a potential for failure of the hydraulic lines connected between the main valve and the cylinder mounted check valve.
One additional difficulty associated with hydraulic cylinders is that on occasion the pressure within the cylinder is elevated to an undesirably high level. Therefore, it is also typical to include a high pressure relief valve that is activated during these undesirable high pressure periods. The pressure relief valve adds additional complexity to the assembly of the hydraulic cylinder. U.S. Pat. No. 4,848,721, issued Jul. 18, 1989, discloses a solenoid controlled pilot operated valve in which the valve elements are grouped into main and pilot sections including a combined seal-bearing means surrounding the main valve member and a solenoid coil integrated into the main valve member.
The present invention is directed to overcoming one or more of these problems as set forth above.